Semiconductor storage device

ABSTRACT

The upper electrode of a capacitor is constituted of laminated films which respectively act as a Schottky barrier layer, a hydrogen diffusion preventing layer, a reaction preventing layer, and an adsorption inhibiting layer. Therefore, the occurrence of a capacitance drop, imperfect insulation, and electrode peeling in the semiconductor device due to a reducing atmosphere can be prevented. In addition, the long-term reliability of the device can be improved.

TECHNICAL FIELD

[0001] The present invention relates to a semiconductor storage deviceand, more particularly, a semiconductor storage device having acapacitor using a high dielectric constant or ferroelectricity.

BACKGROUND ART

[0002] A conventional capacitor using a dielectric having a dielectricconstant higher than that of a silicon oxide film or a ferroelectrichaving a dielectric constant higher than that of a silicon nitride filmhas a large capacitance per unit area. An application requiring a largecapacitance with a small area, particularly, such as a large-scaled DRAMhas been being examined. In the specification, the dielectric having ahigh dielectric constant is defined as a material having a dielectricconstant higher than that of the silicon oxide film. The ferroelectricis a material having a spontaneous polarization which can be inverted byan electric field. In particular, as ferroelectrics, complex-metaloxides such as (Ba, Sr)TiO₃ (hereinbelow, BST) and Pb(Zr, Ti)O₃(hereinbelow, PZT) are being examined. In order to suppress degradationof the oxides upon film formation, a noble metal such as platinum havingoxidation resistance is typically used as a lower electrode. Meanwhile,since an upper electrode is generally formed after film formation, inorder to avoid reaction with the dielectric having a high dielectricconstant in a heat treatment process after formation of a capacitor, theupper electrode is generally made of platinum.

[0003] For example, according to U.S. Pat. No. 5,005,102, a lowerelectrode has a structure of platinum/titanium nitride/titanium and anupper electrode has a structure of aluminum/titanium/platinum. Inparticular, with respect to the upper electrode, it is described thataluminum serves as an electrical contact layer, titanium serves as adiffusion barrier layer against reaction of a diffusion, and platinumserves as a plate layer.

[0004] In case of fabricating a memory using those elements, afterforming a capacitor, a wiring layer for electrically connecting to thecapacitor and a wiring layer related to a peripheral circuit part forperforming electrical conversion between a memory cell and the outsideof the memory chip are formed. In order to obtain electrical insulationbetween the wiring layers and between the wiring layers and thecapacitor, it is necessary to form interlayer insulating films. Thisprocess is performed in a reducing or weak acidic atmosphere in order toprevent degradation of the wiring layers. Since a through hole forelectrically connecting the peripheral circuit and the wiring layersgenerally has a shape of a high aspect ratio, which is deep as comparedwith the size of the opening, tungsten or the like is deposited by CVD.The atmosphere at this time is a reducing one. It is known that thecapacitor is seriously damaged by being subjected to the treatment inthe reducing atmosphere. For example, according to “Material ResearchSociety Symposium Proceedings”, Vol. 310, pp. 151 to 156, 1993, it isreported that by forming an SiO₂ film by CVD, PZT as a ferroelectricloses the ferroelectricity and a leakage current increases.

[0005] Further, although the characteristics of a semiconductor activedevice degrade due to a heat treatment in a capacitor fabricatingprocess, a plasma process in a wiring process, and the like, byadditionally performing a heat treatment in hydrogen at approximately400 degrees after completion of the wiring process, the degradation canbe repaired finally. Consequently, a hydrogen treatment is generallyperformed after completion of the wiring process. It is known that,however, the hydrogen treatment exerts an influence on thecharacteristics of the capacitor in a manner similar to the interlayerinsulating film process. For instance, according to “8th InternationalSymposium on Integrated Ferroelectrics, 11c”, 1996, it is reported that,in the case where SrBi₂Ta₂O₉ (hereinbelow, SBT) is used as aferroelectric, the capacitor is peeled off or, when the capacitor is notpeeled off, a leakage current characteristic largely deteriorates.

[0006] The dielectric having a high dielectric constant and theferroelectric will be generically called a high dielectric constant orferroelectric hereinbelow.

[0007] It is an object of the invention to obtain a very reliablesemiconductor storage device in which the high dielectric constant orferroelectric is prevented from degrading.

DISCLOSURE OF INVENTION

[0008] (Solving Means)

[0009] The object is achieved by providing a capacitor electrode with afilm which reduces an amount of hydrogen molecules reaching thecapacitor electrode to 10¹³/cm² or smaller. It is preferable to use afilm by which the hydrogen molecules become 10¹²/cm² or smaller.

[0010] As a result of examination of the cause of degradation in atreatment using hydrogen, we have found that platinum as an electrode isrelated to a degradation process. Specifically, the following mechanismwas uncovered. When platinum is used as an electrode, hydrogen moleculesare decomposed by platinum, active hydrogen such as hydrogen atoms andhydrogen radicals are generated, and the active hydrogen is promptlydiffused in platinum, thereby degrading the high dielectric constant orferroelectric.

[0011] It was also found out that, because of the existence of themechanism, the capacitor characteristics degrade or an electrode ispeeled off even at a low temperature such as 300° C. At such atemperature, it cannot be usually imagined that the high dielectricconstant or ferroelectric is reduced and degraded.

[0012] By providing a film which prevents hydrogen molecules fromreaching the electrode as much as possible, the high dielectric constantor ferroelectric can be prevented from degrading.

[0013] To be specific, it is sufficient to provide a film whoseadsorption of the hydrogen molecules is 10¹³/cm² or smaller, preferably,10¹²/cm² or smaller. By providing such a film which substantially doesnot adsorb hydrogen (hereinbelow, called an “adsorption inhibitinglayer”), the amount of hydrogen molecules reaching a platinum film as apart of the capacitor electrode is decreased and, as a result, theamount of active hydrogen can be reduced. Thus, degradation and peelingin the wiring forming process of the high dielectric constant orferroelectric capacitor are suppressed and improvement in the long-termreliability is recognized. As a material of the film, silver, aluminum,silicon, lead, bismuth, gold, zinc, cadmium, indium, germanium, and tinare effective. Since the surface of each of these materials has anatomic arrangement which prevents the adsorption of hydrogen, it iseffective in preventing the adsorption. As described above, by providinga layer which does not adsorb hydrogen much as compared with platinum,an effect on suppression of generation of the active hydrogen isproduced. In the case where only an aluminum film is used, since theadsorption of hydrogen is relatively good, it is preferable to furtherprovide a diffusion preventing layer which will be describedhereinbelow. When the films are formed so as to be in contact with theplatinum electrode, mutual diffusion occurs. It is therefore preferableto provide a reaction preventing layer such as a titanium nitride filmor a tungsten nitride film therebetween.

[0014] A film in which the diffusion of hydrogen molecules is 10¹³/cm²or smaller, preferably, 10¹²/cm² or smaller may be provided. Byproviding a film which substantially prevents the diffusion of thehydrogen molecules (hereinbelow, called a “hydrogen diffusion preventinglayer”), the diffusion amount of the hydrogen molecules becomesextremely small, the amount of hydrogen molecules reaching the capacitorelectrode is decreased, and the amount of active hydrogen generated bythe action of the capacitor electrode can be reduced. As a hydrogendiffusion preventing layer, specifically, besides tungsten, a conductiveoxide such as ruthenium oxide, iridium oxide, palladium oxide, osmiumoxide, or platinum oxide, ruthenium, iridium, palladium, osmium, or anoxide of an alloy of any of the materials can be mentioned. In the casewhere the capacitor electrode is made of any of the materials withoutproviding the adsorption inhibiting layer, since the reaction betweenany of the materials and the platinum electrode does not occur so much,it is unnecessary to provide a reaction preventing layer.

[0015] Further, when the capacitor electrode is provided with a stack ofthe adsorption inhibiting layer and the hydrogen diffusion preventinglayer, the amount of hydrogen molecules reaching the capacitor electrodeis further reduced, so that it is more effective. In this case, it issufficient that hydrogen of 10¹²/cm² or smaller reaches the electrodethrough both of the adsorption inhibiting layer and the hydrogendiffusion preventing layer. In the case where the layers are stacked andone of the adsorption inhibiting layer and the hydrogen diffusionpreventing layer is made of an oxide, in order to prevent the reactionbetween the layers, it is preferable to provide a reaction preventinglayer between them. When both of the layers are made of oxides, it isunnecessary to provide the reaction preventing layer.

[0016] The reaction preventing layer may be made of titanium, a titaniumalloy, or a titanium nitride. Besides them, any of tungsten, tantalum,molybdenum, nitrides of the materials, and the like can be used as ahydrogen diffusion preventing layer and reaction preventing layer.

[0017] When the total thickness of the capacitor electrode, the hydrogendiffusion preventing layer, and the adsorption inhibiting layer is 20 nmor more, an effect to a certain extent can be expected. When it exceeds0.5 μm, it becomes difficult to form the structure. Consequently, it ispreferable that the film thickness lies in a range from 20 nm to 0.5 μm.

[0018] The material of the capacitor electrode is not limited toplatinum but may be ruthenium, iridium, palladium, nickel, osmium,rhenium, or a material whose main component is a conductive material ofan oxide of any of these materials.

[0019] Although sufficient effects can be obtained when the hydrogendiffusion preventing layer and the adsorption inhibiting layer areformed in the upper part of the capacitor electrode, it is moreeffective when the layers are formed not only in the upper part but alsoon the sides. Further, when they are formed under the capacitorelectrode, it is effective in preventing invasion of the hydrogenmolecules diffused from the wafer substrate side into the capacitorelectrode. A specific description will be given hereinbelow.

[0020] A capacitor and a semiconductor active device are provided andthe hydrogen diffusion preventing layer is interposed between thecapacitor and the semiconductor active device. It is more preferablethat a hydrogen adsorption preventing layer is disposed on thecapacitor. In the capacitor, two electrodes may be arranged verticallyor horizontally. When the two electrodes are arranged vertically, thehydrogen adsorption inhibiting layer may construct a part of the upperone of the two electrodes.

[0021] It is preferable that a part of the hydrogen diffusion preventinglayer constructs a part of a connection plug which electrically connectsone of the two electrodes to the semiconductor active device.

[0022] Further, it is preferable that a part of the hydrogen diffusionpreventing layer constructs a part of an interlayer insulating filminterposed between the capacitor and the semiconductor active device. Inthis case, preferably, the hydrogen diffusion preventing layer is anoxide insulator. As such a material, for example, a material having themain component of an aluminum oxide or a cerium oxide can be mentioned.The aluminum oxide or cerium oxide can be used by being contained inSiO₂ typically used for the insulating layer. When the aluminum oxide orthe cerium oxide has 5 weight % or more, a certain extent of effect isproduced. When it is 10 weight % or more, more effect is recognized. Theupper limit of the value of the aluminum oxide is regulated from theviewpoint of the workability. The upper limit of the value of the ceriumoxide is regulated from the viewpoint of the insulation performance.

[0023] Further, according to the semiconductor device of the invention,it is preferable that a second semiconductor active device is providedin an area which is different from the area where the capacitor isdisposed and the hydrogen diffusion preventing layer is not formed onthe second semiconductor active device.

[0024] (Effects)

[0025] Defective insulation and peeling of the electrode caused by atreatment in the reducing atmosphere such as metal film CVD and atreatment using hydrogen such as an interlayer insulating film formingprocess can be prevented and the long-term reliability can be improved.

BRIEF DESCRIPTION OF DRAWINGS

[0026]FIG. 1 is a cross section of a capacitor according to anembodiment of the invention, FIG. 2 is a cross section of a capacitoraccording to a prior art, FIG. 3 is a cross section of a capacitoraccording to another preferred embodiment of the invention, FIG. 4 is acharacteristic diagram showing the ratio of electrical breakdown of thecapacitor of the invention and that of the prior art, FIG. 5 is apolarization—voltage characteristic diagram of the capacitor of theinvention and that of the prior art, FIG. 6 is a cross section of acapacitor according to another preferred embodiment of the invention,FIG. 7 is a characteristic diagram showing the comparison of degradationof the capacitance due to an alternating electric field stress betweenthe capacitor of the invention and that of the prior art, FIG. 8 is acharacteristic diagram showing the difference in effects depending onmaterial selection of the invention, FIG. 9 is a partial cross sectionof a DRAM according to the invention, FIG. 10 is a partial cross sectionof a DRAM having a non-volatile operation mode according to theinvention, FIG. 11 is a cross section of a DRAM of an embodiment of theinvention, FIG. 12 is a cross section of a conventional DRAM, FIG. 13 isa diagram showing the comparison between the capacitance of a capacitorwith a hydrogen adsorption and diffusion preventing layer and that of acapacitor without the layer, FIG. 14 is a diagram showing the comparisonbetween an interface state density of a transistor with a hydrogenadsorption and diffusion preventing layer and that of a transistorwithout the layer, FIG. 15 is a diagram showing interface statedensities of the transistor of the invention and the conventionaltransistor, FIG. 16 is a diagram showing electrical breakdowncharacteristics of the capacitors of the transistor of the invention andthe conventional transistor, FIG. 17 is a diagram showing a process offabricating a DRAM of an embodiment of the invention, FIG. 18 is adiagram showing a process of fabricating the DRAM of the embodiment ofthe invention, FIG. 19 is a diagram showing a process of fabricating theDRAM of the embodiment of the invention, FIG. 20 is a diagram showing aprocess of fabricating the DRAM of the embodiment of the invention, andFIG. 21 is a diagram showing a process of fabricating the DRAM of theembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] (Embodiment 1)

[0028] A preferred embodiment of the invention will be describedhereinbelow with reference to FIG. 1.

[0029] In a capacitor of the invention, a lower electrode (102) and ahigh dielectric constant or ferroelectric thin film (103) are formed bya known method on either a device layer or a semiconductor area (101)constructing a transistor, which is formed by a known method. On thefilm (103), an upper layered electrode consisting of four layers of theinvention is formed. That is, the upper layered electrode consists of aSchottky barrier layer (104), a hydrogen diffusion preventing layer(105), a reaction preventing layer (106), and an adsorption inhibitinglayer (107).

[0030] Although the upper layered electrode is comprised of four layersin FIG. 1, the number of stacked layers is decreased by using a layerhaving functions of a plurality of layers or the function of one layercan be realized by a plurality of layers, so that the number of stackedlayers may increase or decrease. All of those numbers are within therange of the invention. A transistor in this case is, specifically, aninsulated gate field effect transistor as a switching element.

[0031] The functions of the layers will now be described. The Schottkybarrier layer (104) serves as a Schottky barrier by being in contactwith the high dielectric constant or ferroelectric layer. The layerserves as the interface between the ferroelectric and the electrode tomake an electron conduction band discontinuous. A leakage current of thecapacitor is reduced by the barrier, so that information holdingcharacteristics necessary for the operation of the semiconductor storagedevice can be obtained. The component elements of the Schottky barrierlayer (103) should not be diffused in the high dielectric constant orferroelectric layer or the Schottky barrier layer (103) should notabsorb the component elements of the high dielectric constant orferroelectric layer by the heat treatment after formation of thecapacitor, and the discontinuous band has to be big enough for theoperation of the semiconductor storage device. The hydrogen diffusionpreventing layer (105) formed after that has the function of effectivelyreducing the concentration of hydrogen reaching the Schottky barrierlayer by suppressing the diffusion of hydrogen which is diffused fromthe upper part.

[0032] The adsorption inhibiting layer (107) which is formed on thehydrogen diffusion preventing layer (105), preferably via the reactionpreventing layer (106), is a layer for checking the hydrogen in agaseous phase. Platinum is usually used for the upper electrode of thehigh dielectric constant or ferroelectric capacitor. It is known thatplatinum has the function of adsorbing and decomposing hydrogen. Thehydrogen once decomposed is easily diffused in a metal, reaches the highdielectric constant or ferroelectric layer, and presents a highreduction performance, so that the capacitor critically deteriorateseven at a low temperature such as 30° C. The adsorption inhibiting layer(107) used here does not adsorb hydrogen and accordingly has no effecton dissociation of hydrogen, so that the probability of injection ofhydrogen into the high dielectric constant or ferroelectric layer isreduced.

[0033] As shown in FIG. 2, a conventional capacitor comprises analuminum (202) as an electrical contact layer, titanium (201) as areaction preventing layer, and platinum as a plate layer and does notproduce an effect on suppressing the diffusion of hydrogen. Although itis known that the aluminum (202) has the function of preventing theadsorption of hydrogen, a sufficient effect cannot be obtained as willbe described hereinlater.

[0034] (Embodiment 2)

[0035] A method of fabricating the layered upper electrode will now bedescribed more specifically.

[0036]FIG. 3 shows a preferred embodiment of a capacitor according tothe invention. On an active device layer (101) including a transistorformed by a known method, platinum (102) is deposited to 100 nm as alower electrode by DC sputtering. Subsequently, PZT is deposited to 50nm by radio frequency sputtering. After that, a heat treatment at 650°C. is performed in oxygen, thereby forming the high dielectric constantor ferroelectric layer (103). 50 nm of platinum (301) is then formed asa Schottky barrier layer. Subsequently, 100 nm of tungsten (302) as adiffusion barrier layer, 50 nm of titanium nitride (303) as a reactionpreventing layer, and 100 nm of silver (304) as an adsorption inhibitinglayer are formed, thereby obtaining a layered upper electrode.

[0037] The electrical breakdown voltage distribution after the heattreatment in hydrogen of the capacitor having the structure is shown inFIG. 4. The capacitor is compared with the prior art of FIG. 2 withrespect to a case where a treatment is performed at 350° C. for thirtyminutes. In the conventional upper electrode structure, most ofcapacitors show defective insulation at 1V to 2V and cannot be appliedto a DRAM. It was found that the capacitor of the invention canpractically withstand in the region up to 1V of an application voltage.The polarization—field characteristics are shown in FIG. 5. Similarly,the hydrogen treatment was performed at 350° C. for thirty minutes.Although the hysteresis characteristic of the polarization—fieldcharacteristic is lost in the prior art, the characteristic can be heldin the present invention. The upper electrode of the capacitor accordingto the prior art was peeled off in the hydrogen treatment at 400° C. Incontrast, according to the invention, there was no peeling anddegradation in the electrical breakdown voltage and the dielectriccharacteristic was a little.

[0038] (Embodiment 3)

[0039] Another preferred embodiment of the invention will be describedwith reference to FIG. 6. On the active device layer (101) including atransistor formed by a known method, platinum (102) is deposited to 100nm as a lower electrode by DC sputtering. Then, on the substrate heatedto 500° C., BST is deposited to 50 nm by the radio frequency sputtering.After that, a heat treatment at 650 ° C. is performed in oxygen, therebyforming a high dielectric layer (601). Subsequently, platinum (301) isdeposited to 50 nm as a Schottky barrier layer. In the embodiment,ruthenium oxide (602) is deposited to 50 nm as a hydrogen diffusionpreventing layer by reactive sputtering using oxygen. On the layer(602), a layered film (603) of 50 nm of metal ruthenium and 50 nm oftitanium nitride is formed in this order as a reaction preventing layerby sputtering. On the layer (603), aluminum (604) is deposited to 100 nmas an adsorption inhibiting layer, thereby obtaining a layered upperelectrode.

[0040] The capacitor having the structure of FIG. 6 is subjected to thehydrogen treatment and the change with time in capacitance was examinedby applying an alternating electric field (FIG. 7). The hydrogentreatment was performed at 400° C. for thirty minutes. Although therewas no change in the initial capacitance also in the prior art shown inFIG. 2 for comparison, the degradation due to the alternating electricfield was severe and the reliability necessary for the semiconductorstorage device could not be assured. It was found that, according to theinvention, the capacitance deteriorates slightly and the reliability canbe assured.

[0041] Another preferred materials and fabrication methods of thelayered upper electrode of the invention will now be described. Althoughthe Schottky barrier layer is made of platinum in the above examples, amaterial containing any of ruthenium, iridium, palladium, nickel, andplatinum as the main component is suitable. As the hydrogen diffusionpreventing layer, besides tungsten and ruthenium oxides, a conductiveoxide, preferably, iridium oxide or palladium oxide can be applied. Asthe reaction preventing layer, besides titanium nitride, titanium or atitanium alloy is applicable. A metal selected from tungsten, tantalum,and molybdenum or a nitride of any of the metals can be used as ahydrogen diffusion preventing layer and the reaction preventing layer.In the case where the conductive oxide is used as the hydrogen diffusionpreventing layer, it is necessary to use a layer made of, as the maincomponent, a metal which makes an oxide conductive as a barrier layeragainst oxygen in the conductive oxide. Preferably, platinum, iridium,ruthenium, or palladium is used. Although silver and aluminum werementioned as examples as the hydrogen adsorption inhibiting layer, aconductor containing silver, aluminum, silicon, lead, or bismuth as themain component is suitable. The action, however, largely variesaccording to the materials. FIG. 8 illustrates a case using silver andaluminum as an adsorption inhibiting layer for comparison of a change inthe switching charge amount of PZT by hydrogen annealing. A case ofusing, not the layered film, but only the Schottky barrier layer made ofplatinum is shown for comparison. The effect of the case using aluminumis smaller as compared with silver. It is understood that a damagecaused by hydrogen cannot be suppressed by the conventional structureshown in FIG. 2.

[0042] Although BST and PZT have been mentioned above as examples of thehigh dielectric constant or ferroelectric material, high electricconstant or ferroelectric materials of oxides each having, as the maincomponent, an element selected from barium, lead, strontium, and bismuthare effective. Preferable materials except for BST and PZT are strontiumtitanate (SrTiO₃), lead titanate (PbTiO₃), barium lead zirconatetitanate ((Ba, Pb) (Zr, Ti)O₃), barium lead niobate ((Ba, Pb)Nb₂OQ₆),strontium bismuth tantalate (SrBi₂Ta₂O₉), and bismuth titanate(Bi₄Ti₃O₁₂).

[0043] (Embodiment 4)

[0044] Examples of the semiconductor storage devices having thecapacitors will now be described.

[0045]FIG. 9 relates to an example of a DRAM using BST as a highdielectric constant or ferroelectric layer. On an Si substrate (1001),device layers including transistors are formed by a known process.Specifically, an isolation film (1002), a conductive impurity diffusionlayer (1003), a polysilicon transistor gate electrode (1004), apolysilicon wiring (1005), and an interlayer insulating film (1006) areformed. A conductive plug (1007) for obtaining electric connectionbetween the capacitor and transistor is formed. Preferably, the materialof the conductive plug (1007) is either a titanium nitride/titaniumsilicide stacked layer or a titanium nitride/polysilicon stacked layerformed by CVD. Subsequently, platinum is deposited to 100 nm by the DCsputtering and, after that, the platinum is processed by argonsputtering with a mask pattern formed by known photolithography, therebyforming a platinum lower electrode (1008). Then, a BST film (1009) isformed by, preferably, CVD for performing thermal decomposition inoxygen by using an alcoholate or complex of barium, strontium, ortitanium. More preferably, CVD using di-pyvaroyle methanate barium(Ba(DPM)₂), di-pyvaroyle methanate strontium (Sr(DPM)₂), and titaniumisopropoxide (Ti(i-OC₃H₇)₄) is effective. These materials are charged ina heat insulating vessel. Ba(DPM)₂ and Sr(DPM)₂ are heated to 150° C. to250° C. and Ti (i-OC₃H₇)₄ is heated to 30° C. to 60° C. so as to have aproper steam pressure. The materials are transported into a reactionchamber by argon bubbling. With oxygen simultaneously supplied to thereaction chamber, the materials are thermal decomposed and oxidized on asubstrate heated to 400° C. to 700° C. The thickness of the BST film isset to 20 nm. Platinum is deposited to 100 nm by sputtering as aSchottky barrier layer (1010) In this case, depending on the aspectratio of a trench between the lower electrodes, sputtering and etch backso as to direct platinum particles or formation of ruthenium by CVD isnecessary. As a part of the hydrogen diffusion preventing layer and thereaction preventing layer, an iridium/iridium oxide stacked film (1011)is formed. In this case, a stacked film of iridium oxide by reactivesputtering by mixing with oxygen and metal iridium by typical argonsputtering is formed. Subsequently, titanium nitride (1012) is depositedto 50 nm as a reaction preventing layer by reactive sputtering by mixingwith nitrogen. Finally, as a hydrogen adsorption inhibiting layer,silver (1013) is deposited to 20 nm by sputtering, thereby forming thelayered upper electrode for capacitor according to the invention. Asshown in FIG. 9, in the structure of the upper electrode according tothe invention, it does not have to be divided into information bits. Thestructure such that the capacitor is covered with the upper electrodefor a plurality of bits can be realized. The covered structure shown inthe diagram is more effective. With the structure, even in the case ofthe upper electrode having a complicated layered structure, applicationof micro processing with a processing accuracy which is not strict canbe realized irrespective of the minimum processing dimension of aproduct of the generation such as a control gate of a transistor.

[0046] A wiring process after formation of the capacitor will now bedescribed. An interlayer insulating film (1014) having the thickness of200 nm is formed by known plasma CVD using tetra ethyloxy silane (TEOS).An electrical contact hole (1016) is opened by dry etching. A connectionplug is inserted into the contact hole (1016) by known hydrogen reducingblanket tungsten CVD. In this case, deposition is performed for aboutthirty seconds by using tungsten hexafluoride and hydrogen with thesubstrate temperature of 400° C. and the pressure of 0.5 Torr. In thecase of the known upper electrode structure, namely, the layeredelectrode of aluminum, titanium nitride, and platinum, degradationoccurs in the electrical breakdown voltage by the CVD in a mannersimilar to FIG. 4. After formation of the tungsten connection plug, aplanarization process is performed and, further, a layered wiring (1017)of titanium nitride and aluminum is formed. An interlayer insulatingfilm (1018) is then formed so as to cover the layered wiring (1017). Inthe case of further providing a wiring layer as well, theabove-mentioned wiring process after completion of formation of thecapacitor can be applied. The electrical breakdown voltage of thecapacitor deteriorated severely in the electrode having the conventionalstructure also in the case where the hydrogen heat treatment aftercompletion of the wiring process was performed at 400° C. for thirtyminutes. On the contrary, according to the invention, thecharacteristics after formation of the layered upper electrode could beheld. The final capacitance of the capacitor was 90 fF/μm² and thecritical voltage of the insulation performance defined as 10−8A/cm² was1.2V. Although there are two capacitors in FIG. 9, also in the case ofthree or more capacitors, it is sufficient to form a protection film soas to cover the capacitors in a manner similar to the above.

[0047]FIG. 10 illustrates an example of a DRAM having a non-volatileoperating mode using PZT as a high dielectric constant or ferroelectric.In a manner similar to the case of BST-DRAM, the device layers includingtransistors are formed by a known method. Then, titanium nitride isdeposited by reactive sputtering to 50 nm as a layer (1101) forpreventing the reaction between a lower electrode (1102) and theconductive plug (1007). Subsequently, platinum serving as the lowerelectrode (1102) is deposited to 150 nm by DC sputtering and 50 nm ofPZT is formed. In order to deposit PZT, the sputtering, sol-gel method,reactive deposition, and CVD can be applied. For example, it ispreferable to perform the CVD by using an alcoholate or complex of lead,zirconium, and titanium and thermal decomposing it in oxygen. Morepreferably, a method using di-pyvaroyle methanate lead (Pb(DPM)₂),di-pyvaroyle methanate zirconium (Zr(DPM)₄), and titanium isopropoxide(Ti(i-OC₃H₇)₄) is effective. These materials are charged in a heatinsulating vessel. Pb(DPM)₂ is heated to 100° C. to 150+ C., Zr(DPM)₄ isheated to 150° C. to 200° C., and Ti(i-OC₃H₇)₄ is heated to 30° C. to60° C. so as to have a proper steam pressure. The materials aretransported into a reaction chamber by argon bubbling. With oxygensimultaneously supplied to the reaction chamber, the materials arethermal decomposed and oxidized on a substrate heated to 500° C. to 700°C. The thickness of the PZT film is set to 40 nm.

[0048] Subsequently, platinum is deposited to 50 nm as a Schottkybarrier layer (1104) by DC sputtering and tungsten serving as a hydrogendiffusion preventing layer (1105) is deposited to 100 nm by DCsputtering. After that, a pattern in the capacitor area is formed by aknown photolithography technique and the capacitor is divided into bitsby dry etching. Then, a capacitor protection film (1107) is formed by aknown heat decomposition in the ozone atmosphere of tetra ethyloxysilane (TEOS) and etched back. Further, by a known photolithographytechnique, electrical contact holes to the capacitor are opened. On thefilm (1107), tungsten is deposited as a hydrogen diffusion preventinglayer (1106) by sputtering while filling the electrical contact holes.Titanium nitride is deposited to 50 nm as a reaction preventing layer byreactive sputtering and, finally, silver is deposited to 50 nm as theadsorption inhibiting layer (1013). By the processes, the capacitor ofthe invention is formed on the device layer.

[0049] A wiring process after formation of the capacitor is similar tothat of the BST-DRAM. At the time of formation of a tungsten connectionplug (1016), in the case of the conventional aluminum/titanium/platinumstacked structure, a number of peelings occur in the interface of theSchottky barrier layer (1104) and the PZT (1103) and the structure isnot practically used. On the other hand, in the case of using thestructure of the invention, no peeling occurs and the degradation of aresidual polarization is suppressed. The final residual polarization is10 μC/cm² during operation at the source voltage of 3V. A non-residualpolarization component was 20 μC/cm².

[0050] (Embodiment 5)

[0051] A preferred embodiment of the invention will be described withreference to FIG. 11. FIG. 11 relates to a case where the invention isapplied to the DRAM. A memory cell transistor (2) and a peripheraltransistor (3) are formed as semiconductor active devices on a siliconsubstrate (1). The memory cell transistor (2) is a semiconductor activedevice which is formed lower than a capacitor for storing informationcomprised of a lower electrode (8), a high dielectric constant orferroelectric (9), and an upper electrode (10). The peripheraltransistor (3) is a semiconductor active device formed separately fromthe capacitor area.

[0052] An interlayer insulating layer (4) is interposed between thecapacitor layer and the transistor layer so as to electrically insulatethe layers from each other. The capacitor layer and the transistor layerare electrically connected via plugs. Each plug is made up of two layersof a first plug (5) and a second plug (6). The second plug (6) is madeof a conductive oxide whose degree of hydrogen diffusion is lower thanthat of the first plug (5). Between the interlayer insulating layer (4)and the capacitor layer, a hydrogen diffusion preventing layer (7) madeof an insulating material having the degree of hydrogen diffusion lowerthan that of the interlayer insulating layer (4) is interposed. In theuppermost part of the upper electrode (10) of the capacitor layer, ahydrogen adsorption preventing layer (11) is provided. An interlayerinsulating layer (12) insulated from an upper wiring layer (14) and aconnection plug (13) are also provided.

[0053] The structure of a conventional DRAM is shown in FIG. 12. Thepoint different from the conventional DRAM is that, in the DRAM (FIG.11) of the invention, the capacitor is protected from reduction causedby hydrogen by the hydrogen adsorption preventing layer (11), the secondplug (6) made of the conductive oxide, and the hydrogen diffusionpreventing layer (7) made of an insulating material.

[0054] The effects of the invention will now be described. The capacitorin the structure illustrated in FIG. 12 is very sensitive to a damagecaused by hydrogen. For example, when a hydrogen heat treatment at 350°C. for approximately ten minutes is performed, both of the dielectricconstant and the electrical breakdown voltage largely decrease. On thecontrary, when the hydrogen adsorption preventing layer which is thesame as that shown in FIG. 11 is provided on the upper electrode,degradation of the dielectric constant and the electrical breakdownvoltage is suppressed (FIG. 13). By providing the hydrogen adsorptionpreventing layer, however, as shown in FIG. 14, the interface state inthe gate part of the transistor did not sufficiently recover even by thehydrogen heat treatment. This is because active hydrogen does not easilyreach the gate part of the transistor. Especially, in the peripheraltransistor, since the gain of the transistor is decreased, the ONcurrent in the initial design cannot be assured. A problem such thataccess time of the storage device becomes longer consequently occurs.

[0055] In contrast, according to the capacitor of the DRAM of theinvention, the hydrogen adsorption inhibiting layer (11) in theuppermost part of the upper electrode is provided so as to cover onlythe memory cell transistor which demands a relatively low gain of thetransistor. Further, by the functions of the second plug (6) and thehydrogen diffusion preventing layer (7) disposed under the capacitor,degradation of the capacitor caused by hydrogen diffused in the lateraldirection is suppressed. As a result, as shown in FIG. 15, a sufficienthydrogen heat treatment can be applied so that the interface statedensity can be decreased in both of the memory cell transistor and theperipheral transistor. In FIG. 15, the curve with the hydrogenadsorption inhibiting layer shows the case where the hydrogen adsorptioninhibiting layer is provided on both of the memory cell transistor andthe peripheral transistor. Each of the curve of the memory celltransistor and the curve of the peripheral transistor indicates theeffective interface state density of each transistor in the case wherethe hydrogen adsorption inhibiting layer is disposed on only the memorycell transistor.

[0056]FIG. 16 shows the comparison between a change in the electricalbreakdown voltage of the capacitor when the heat treatment was performedfor thirty minutes in the case where the second plug (6) and thehydrogen diffusion preventing layer (7) are provided under the capacitorand that in the case where the second plug (6) and the hydrogendiffusion preventing layer (7) are not provided. It is understood that,in the prior art, degradation in the electrical breakdown voltage of thecapacitor occurs due to the diffusion in the lateral direction andrecovery of the characteristics of the transistor and holding of thecharacteristics of the capacitor have the trade-off relation. On theother hand, according to the invention, the degradation in theelectrical breakdown voltage is suppressed within a memory applicablerange and the trade-off can be avoided.

[0057] (Embodiment 6)

[0058] A method of fabricating the semiconductor device will now bedescribed more specifically.

[0059] First, as illustrated in FIG. 17, the memory cell transistor (2)and the peripheral transistor (3) are formed by a known method on thesilicon substrate (1). After the interlayer insulating layer (4)including wiring which interconnects transistors is formed, the hydrogendiffusion preventing layer (7) under the capacitor is formed. As thematerial, a material which suppresses diffusion of hydrogen more thanthe insulating film having SiO₂ as the main component which is usuallyused as an interlayer insulating layer, preferably, an aluminum oxidecan be used. As another material, a cerium oxide can be mentioned. AnSiO₂ oxide containing the above materials may be also used. Theperipheral transistor part in the hydrogen diffusion inhibiting layer isremoved after film formation (FIG. 18).

[0060] Subsequently, contact holes for plugs electrically connecting thecapacitor to the memory cell transistor are opened by dry etching.Although the contact hole is opened also in the peripheral transistorpart as necessary, this is selectively done according to the difficultyin processing of the contact hole of the connection plug (13) in FIG. 13and is not related to the essence of the invention. Then, the contacthole is subjected to a plug embedding process. By CVD of excellent stepcoverage, preferably after formation of a layer of titanium nitride orpolysilicon, the first plug (5) is formed first by etch back.Subsequently, the second plug (6) as a conductive hydrogen diffusioninhibiting layer is formed on the whole surface. Iridium oxide is usedhere. As other preferable materials, ruthenium oxide, osmium oxide,platinum oxide, or a mixture of them can be mentioned (FIG. 19).

[0061] The hydrogen diffusion preventing layer formed on the wholesurface is removed except for the plug parts by etch back orchemical-mechanical polishing. After that, the lower electrodes (8) areformed. Although platinum is used as the material of the lower electrodehere, ruthenium, iridium, osmium, rhenium, and a conductive materialhaving the material selected from oxides of those materials as the maincomponent are suitable. Any of the materials is deposited to 150 nm bysputtering and, after that, the film is divided into memory elements,thereby obtaining the lower electrode structure (FIG. 20).

[0062] BST is then deposited as a high dielectric constant orferroelectric (9) by CVD so as to have the thickness of 30 nm. BST isformed by introducing di-pyvaroyle methanate barium (Ba(DPM)₂),di-pyvaroyle methanate strontium (Sr(DPM)₃), and titanium isopropoxide(Ti(i-OC₃H₇)₄) into a reactive chamber by bubbling and thermaldecomposing the materials in an oxidizing atmosphere. As the material ofthe CVD, besides the above materials, a known complex or alkoxide can beused. For introduction of the materials, a method using determination ofliquid materials and a carburetor may be also used. As a method ofdecomposition, besides the heat decomposition, plasma assist can beused. After formation of the BST film, a heat treatment is performed inoxygen or nitrogen as necessary.

[0063] Subsequently, as the upper electrode (10), Ru is deposited tohave the thickness of 100 nm by CVD. As the material of the upperelectrode, the materials used for the lower electrode, that is,platinum, iridium, osmium, rhenium, and a conductive material having thematerial selected from oxides of those materials as the main componentare suitable. In this case, a ruthenium thin film serving as an upperelectrode is formed by thermal decomposition CVD in the oxygenatmosphere using ruthenocene as a row material. After formation of theupper electrode, a heat treatment is carried out in oxygen or nitrogenas necessary.

[0064] The upper electrode/BST stacked film is processed by dry etchingso as to leave the memory cell part and the adsorption inhibiting layer(11) is formed by the CVD. Aluminum is used as a material having lowhydrogen adsorptivity and diffusivity. It is sufficient to use thematerial having the hydrogen adsorptivity and diffusivity lower thanthose of the upper electrode (10) and the lower electrode (8) for theadsorption and diffusion inhibiting layer (11). As examples, there aregold, silver, aluminum, silicon, silver, zinc, cadmium, indium,germanium, tin, lead, and bismuth. Especially, aluminum, silicon, andlead are suitable. The film is removed except for the memory celltransistor parts by the dry etching, thereby obtaining the structureshown in FIG. 21.

[0065] After that, the interlayer insulating film (12) is formed by theCVD. As described above, due to the actions of the adsorption inhibitinglayer (11), the hydrogen diffusion preventing layer (7), and the secondplug (6), known plasma CVD or thermal CVD can be used as CVD. In thecase where there is no adsorption inhibiting layer (11), capacitancereduction, electrical breakdown voltage degradation, and electrodepeeling of the capacitor occur at this time point, so that a memorycannot be produced. For the interlayer insulating film (12), the wiringlayer (14) and the connection plug (13) for electrically connecting thewiring layer (14) to the transistor are formed, thereby obtaining thestructure illustrated in FIG. 21. Especially, as an effect of theinvention, it can be mentioned that the connection plug (13) can beformed by selective CVD using a silane gas and hexafluoride tungsten. Byperforming hydrogen annealing in the state of FIG. 21, thecharacteristics of the memory cell transistor (2) and the peripheraltransistor (3) are repaired. The parameters are such that the hydrogenannealing is performed in 3% hydrogen atmosphere at 400° C. for thirtyminutes. In this case as well, as mentioned above, degradations as shownin FIGS. 13 to 15 occur and the memory operation cannot be executed inthe conventional structure.

[0066] As an example of the high dielectric constant or ferroelectricmaterial, BST has been mentioned. With strontium titanate (SrTiO₃) aswell, almost similar effects are obtained. Except for this, an oxidehigh dielectric constant or ferroelectric material having, as the maincomponent, an element selected from barium, lead, strontium, and bismuthis effective. Especially, when any of PZT, lead titanate (PbTiO₃),barium lead zirconate titanate ((Ba, Pb) (Zr, Ti)O₃), barium leadniobate ((Ba, Pb)Nb₂O₆), strontium bismuth tantalate (SrBi₂Ta₂O₉), andbismuth titanate (Bi₄Ti₃O₁₂) is used, a memory having a non-volatilefunction can be formed.

[0067] The final capacitance of the capacitor using BST is 6.5 μF/cm²(in the event of operation at the source voltage of 2.2V) and an averageelectrical breakdown voltage is 3V.

[0068] Industrial Applicability

[0069] The present invention is applied to a memory device having astorage capacity part, for example, a dynamic random access memory orthe like.

1. A semiconductor storage device characterized by comprising: acapacitor having a first electrode, a high dielectric constant orferroelectric film, and a second electrode; and a fourth film by whichan amount of hydrogen molecules reaching the second electrode becomes10¹³/cm² or less.
 2. A semiconductor storage device according to claim1, characterized in that the fourth film is provided on the capacitor.3. A semiconductor storage device according to claim 1 or 2,characterized in that the fourth film is provided on the sides of thecapacitor.
 4. A semiconductor storage device according to any one ofclaims 1 to 3, characterized in that the second electrode has, as themain component, any of platinum, palladium, ruthenium, iridium, nickel,osmium, rhenium, and a conductive material of an oxide of any of thematerials.
 5. A semiconductor storage device characterized bycomprising: a capacitor having a first electrode, a high dielectricconstant or ferroelectric film, and a second electrode; and a fourthfilm by which an amount of hydrogen molecules reaching the secondelectrode becomes 10¹²/cm² or less.
 6. A semiconductor storage deviceaccording to claim 5, characterized in that the fourth film is providedon the capacitor.
 7. A semiconductor storage device according to claim 5or 6, characterized in that the fourth film is provided on the sides ofthe capacitor.
 8. A semiconductor storage device according to any one ofclaims 5 to 7, characterized in that the second electrode has, as themain component, any of platinum, palladium, ruthenium, iridium, nickel,osmium, rhenium, and a conductive material of an oxide of any of thematerials.
 9. A semiconductor storage device characterized bycomprising: a storage capacity part having a first conductive materialfilm, a high dielectric constant or ferroelectric film, and a secondconductive material film; and a fourth film provided for the storagecapacity part, whose adsorption of hydrogen molecules is 10¹²/cm² orless.
 10. A semiconductor storage device according to claim 9,characterized in that the fourth film is provided on the storagecapacity part.
 11. A semiconductor storage device characterized bycomprising: a storage capacity part having a first conductive materialfilm, a high dielectric constant or ferroelectric film, and a secondconductive material film; and a film which is provided for the storagecapacity part and is made of any of silver, silicon, lead, bismuth,gold, zinc, cadmium, indium, germanium, and tin.
 12. A semiconductorstorage device characterized by comprising: a storage capacity parthaving a first conductive material film, a high dielectric constant orferroelectric film, and a second conductive material film; and a fourthfilm provided for the storage capacity part, whose diffusion of hydrogenmolecules is 10¹²/cm² or less.
 13. A semiconductor storage deviceaccording to claim 12, characterized in that the fourth film is providedon the storage capacity part.
 14. A semiconductor storage devicecharacterized by comprising: a storage capacity part having a firstconductive material film, a high dielectric constant or ferroelectricfilm, and a second conductive material film; and a film which isprovided for the storage capacity part and is made of any of tungsten,ruthenium, iridium, palladium, osmium, ruthenium oxide, iridium oxide,palladium oxide, osmium oxide, platinum oxide, and an oxide of an alloyof any of tungsten, ruthenium, iridium, palladium, and osmium.
 15. Asemiconductor storage device characterized by comprising: a storagecapacity part having a first electrode, a high dielectric constant orferroelectric film which is provided in contact with the firstelectrode, and a second electrode provided in contact with the highdielectric constant or ferroelectric film; a hydrogen diffusionpreventing layer provided on the storage capacity part; and anadsorption inhibiting layer provided on the hydrogen diffusionpreventing layer.
 16. A semiconductor storage device according to claim15, characterized in that a reaction preventing layer is providedbetween the hydrogen diffusion preventing layer and the adsorptioninhibiting layer.
 17. A semiconductor storage device according to claim15 or 16, characterized in that the adsorption inhibiting layer is alayer made of any of silver, aluminum, silicon, lead, bismuth, gold,zinc, cadmium, indium, germanium, and tin.
 18. A semiconductor storagedevice according to any one of claims 15 to 17, characterized in thatthe hydrogen diffusion preventing layer is a layer made of any oftitanium, tungsten, tantalum, molybdenum, an alloy or nitride of any ofthese materials, tungsten, ruthenium, iridium, palladium, osmium,ruthenium oxide, iridium oxide, palladium oxide, osmium oxide, platinumoxide, and an oxide of an alloy of any of tungsten, ruthenium, iridium,palladium, and osmium.
 19. A semiconductor storage device according toclaim 16, characterized in that the reaction preventing layer is made ofany of titanium, tungsten, tantalum, molybdenum, or an alloy or nitrideof any of these materials.
 20. A semiconductor storage device accordingto claim 15, characterized in that the hydrogen diffusion preventinglayer or the adsorption inhibiting layer is made of a conductive oxideand a reaction preventing layer is provided between the hydrogendiffusion preventing layer and the adsorption inhibiting layer.
 21. Asemiconductor storage device according to any of claims 15 to 20,characterized in that the high dielectric constant or ferroelectric filmis made of an oxide having, as the main component, any of barium, lead,strontium, bismuth, and titanium.
 22. A semiconductor storage deviceaccording to claim 21, characterized in that the high dielectricconstant or ferroelectric film is made of barium strontium titanate orlead zirconate titanate.
 23. A memory characterized by comprising: atransistor provided for a substrate; a storage capacity part having ahigh dielectric constant or ferroelectric film provided on thesubstrate; and a fourth film provided on the storage capacity part, bywhich an amount of hydrogen molecules reaching the storage capacity partbecomes 10¹³/cm² or less.
 24. A memory characterized by comprising: atransistor provided for a substrate; a storage capacity part having ahigh dielectric constant or ferroelectric film provided on thesubstrate; and a hydrogen diffusion preventing layer provided on thestorage capacity part and an adsorption inhibiting layer provided on thehydrogen diffusion preventing layer.
 25. A semiconductor storage devicecharacterized by comprising: an active device; a capacitor having afirst electrode, a second electrode, and a high dielectric constant orferroelectric film provided between the first and second electrodes; anda hydrogen diffusion preventing layer formed between the active deviceand the capacitor.
 26. A semiconductor storage device according to claim25, characterized in that an adsorption inhibiting layer is provided onthe capacitor.
 27. A semiconductor storage device according to claim 25or 26, characterized in that an adsorption inhibiting layer is providedon the sides of the capacitor.
 28. A semiconductor storage deviceaccording to claim 26 or 27, characterized in that the adsorptioninhibiting layer constructs a part of the second electrode.
 29. Asemiconductor storage device according to any one of claims 26 to 28,characterized in that the adsorption inhibiting layer and the hydrogendiffusion preventing layer are formed so as to be in contact with eachother around the capacitor.
 30. A semiconductor storage devicecharacterized by comprising: an active device; an insulating film formedon the active device; an opening formed in the insulating film; a plugwhich is formed in the opening and has a hydrogen diffusion preventinglayer electrically connecting to the active device; and a storagecapacity part which is formed on the hydrogen diffusion preventing layerand has a high dielectric constant or ferroelectric film.
 31. Asemiconductor storage device characterized by comprising: an activedevice; an insulating film which is formed on the active device and in apart of which a hydrogen diffusion preventing layer is formed; and astorage capacity part having a high dielectric constant or ferroelectricfilm formed on the insulating film.
 32. A semiconductor storage deviceaccording to claim 31, characterized in that the hydrogen diffusionpreventing layer is an oxide insulator.
 33. A semiconductor storagedevice according to claim 32, characterized in that the oxide insulatoris made of a material having an oxide of aluminum or cerium as the maincomponent.
 34. A semiconductor storage device characterized bycomprising: a first transistor; a storage capacity part having a highdielectric constant or ferroelectric film; and a hydrogen diffusionpreventing layer which is formed between the first transistor and thestorage capacity part and which is not formed on the second transistor.